Athlete preparation is a hugely diverse area with many different factors contributing to producing the best possible performance on any given occasion. It is the norm to see player preparation centred around the physiological aspect of performance, whether that is muscular or any other physiological aspect. Consequentially, a factor, which may often be overlooked, is hydration; to be more specific, hydration and its subsequent effect on cognitive function.

In most sports the ability to solve problems, have quick reactions and sharp observations is paramount to success. It has been shown that hypohydration (dehydration), defined by Kleiner (1999) and Ganio et al. (2011) as a 1% reduction in body weight following activity or exposure to extreme environments. Wilson et al. (2003) state that dehydration is a reliable predictor of cognitive impairment.

Wilson et al. (2003) is supported by the literature, which, points to a positive relationship between hypohydration and a reduction in cognitive performance (Suhr et al., 2004; Edmonds et al., 2009; Secher et al., 2012; Fadda et al., 2012). In the body of the literature hypohydration is caused by exposure to extreme heats without rehydration being permitted. As a consequence, when dealing with athletes who are required to perform in high temperatures it is important to maintain normal hydration levels (euhydration) as to ensure optimal cognitive function. This is especially important when considering the data presented by Secher et al. (2012), which highlighted rehydration post event does not improve cognitive performance any quicker than maintaining a dehydrated state. Furthermore Edmonds et al. (2009) studied the effects of hyperhydration on cognitive performance and found that there was an improvement in cognitive performance when the subjects over consumed water. This affirms the notion that maintaining euhydration is paramount to cognitive function. Furthermore the findings of Edmonds et al. (2009) suggest that hyperhydration, to a certain degree, be less dangerous that hypohydration in relation to cognitive performance.

Alongside those who perform in extreme climates, there are, as ever, at risk populations. One of those is children. Fadda et al. (2012) focussed a study on a child sample and found that cognitive functions such as short-term memory were compromised. This is mirrored by Secher et al. (2012) and Suhr et al. (2004) who both found that short term memory was compromised when hypohydrated.

Little evidence is available to demonstrate the effect of hypohydration in real sporting scenarios however Adam et al. (2005) researched the effect of hypohydration on army field exercises. Although not a direct link to sport, the real life application of the research allows for conclusions to be drawn. Adam et al. (2005) state that in cold temperatures a dehydration of 3% body weight did not impair cognitive function. It has been shown in the research that those who were acclimatised to hot conditions did not demonstrate any adverse effects relating to cognitive function when dehydrated.

To apply this, it could be suggested that when dealing with sports that travel to hot climates to perform, a period of acclimatisation would be beneficial to help offset any potential decline in cognitive performance. Another potential beneficial practical application of the literature would be to allow for regular hydration breaks so maintain player euhydration reducing the need for extensive rehydration, shown by Secher et al. (2012) as to be ineffective. Aside from direct performance applications, Ganio et al. (2011) highlights how mood and affect may be influenced through dehydration. As a consequence, knowing your athlete as a coach is extremely important. In doing so, it may be possible to highlight mood changes and relate that to dehydration, preventing potential cognitive impairments before they can manifest. In essence, it is essential to recognise symptoms early, and respond whilst promoting good hydration at all times to your athletes as to reap the greatest cognitive and psychological rewards.